It is often desirable to survey or “log” the formations surrounding a borehole by passing a logging sonde or well logging tool through the borehole to measure the parameters or characteristics of the formations at various depths within the borehole. The logging tool is passed through the borehole using a wireline cable which supplies electrical power to the logging tool and transmits telemetry signals between the surface and the logging tool. The logging tool collects data and other information as it passes through the borehole and transmits the data and information to the surface for further processing and analysis.
One popular multiconductor wireline cable comprises six insulated conductors wrapped around a seventh, central insulated conductor. This assembly is encased within two counter-wound layers of steel armor wires which protect the interior conductors and carry the weight of the cable and sonde. Such an assembly may be used to transfer power to logging tools downhole while providing the capability for bi-directional, full-duplex telemetry between the tools and a computer at the surface. However, if one of these conductors develops electrical leakage to armor (or opens such that it can no longer pass current), then the assembly becomes unstable and fails to transfer the required power to the tools downhole. The telemetry system also may fail to accurately transmit and receive data. Thus, there is a need for a power delivery system for wireline logging that is capable of continued power and data delivery even if part of the system has been damaged.